The present invention relates to a release equipment or accessory for a rotating drill string, said drill string release accessory being adapted for activation in order to release and disengage the drill string, e.g. upon a wedged bit situation or other situations where an accessory is stuck in a bottom hole position.
At high drilling speeds, e.g. 100 meters per hour, there exists a particularly great risk for the bit to get wedged and stuck in the formation in which drilling is carried out. There are examples where several thousand metres of drilled hole have been lost in connection with such wedged and unsuccessful drill string release situations. When such situations arise, it is important to have the drill string released as rapidly as possible and, thereafter, to return to ordinary drilling without having lost too much old bore hole.
If the bit wedges itself or get stuck in some other way in the formation in which drilling is carried out, one will, at first, try to pull the bit free in an upward direction, by means of the drill string. Often, this cannot be done and, therefore, in order to get the drill string released, explosives in the form of an explosive charge suspended from a wire are pumped down to the place where the bit is wedged, in order to free the stuck bit through blasting to pieces a drill string portion above the stuck bit.
Thus, conventional and other known technology comprises, first of all, the use of explosives and the utilization of blasting technique. Primarily, this is time-consuming because it takes time to mobilize accessories and personnel. Additionally, the blasting in itself represents a risk moment, namely upon unintentional blasting to pieces the surrounding formation and destructing old bore hole.